1. Field of the invention:
The present invention relates to an electronic flash photographing system, and more particularly to an electronic flash photographing system in which many items of information can be transmitted between a camera and a flash lamp through a small number of signal transmission paths.
2. Description of the Prior Art:
Electronic flash devices (hereinafter referred to as "strobe") are roughly classified into built-in strobes integral with cameras and independent strobes separate from cameras. In general, more independent strobes are popular among users than built-in strobes since the built-in strobes tend to fail to produce a sufficient amount of light output and exhibit a disadvantage in sophisticated flash techniques such as bounce flash.
The independent strobe requires a wire or terminal for transmitting items of information between the strobe and the camera since the strobe and the camera are separate from each other. The wire or terminal used heretofore for such signal transmission between the strobe and the camera is known as a hot shoe (or direct shoe) or a synchro-cord. The hot shoe or the like transmits a light-emission signal or a light-emission stop signal from the camera to the strobe, and also transmits, from the strobe to the camera, a signal representative of the completion of charging of a main capacitor in the strobe or a signal indicating whether proper flash control has been effected in an automatic flash control strobe. In actual strobe photography, much more items of information are required to be transmitted between the camera and the strobe. For example, strobe control or automization can be rendered effective by transmitting information on a guide number setting and an automatic/manual mode setting, information on an F number setting, information indicating a general strobe or a dedicated strobe, information on a subject distance, a strobe light-emission start signal and a strobe light-emission stop signal, and other pieces of information.
To transmit the conventionally required pieces of information, three to four connecting terminals or wires are required, but cannot easily be connected by a hot-shoe connector arrangement. For the transmission of more items of information, the number of terminals needed to electrically connect the strobe and the camera is increased to the point where the connection can no longer be achieved by the hot-shoe connector. The strobe with a required connector arrangement for such information transmission would not be handled easily, and would not be compatible with different cameras, but would only be usable exclusively with the camera to which the strobe is connected.
Among the various information signals referred to above, the strobe light-emission stop signal from the camera is produced by a light control means mounted on a camera and composed of a light detector, an integrator, and other circuits. In particular, a direct photometric system in which strobe light falling upon a film surface through a photographic lens is measured by a light detector generates a light-emission stop signal having a higher light control accuracy than that of a light-emission stop signal produced by a light control means mounted on a strobe. The conventional electronic flash photographing system has an extra signal transmission terminal or a signal wire for transmitting the above light-emission stop signal generated in the camera to the strobe, imposing a limitation on the transmission of the other signals or resulting in the foregoing drawbacks.
It would be possible to manually switch between light control by the light control means on the strobe and light control by the light control means on the camera. However, such a manual switching attempt would be quite troublesome and invite an error or would not be reliable as the user might forget to effect the switching.
There are instances in which when a strobe is mounted on a camera and the camera is ready for strobe photography or in a strobe photographic mode, a subject to be photographed is bright enough not to require light emission from the strobe, or limit emission from the strobe is harmful as when taking a television image. In such instances, the camera or the strobe should be brought from the strobe photographic mode into a normal photographic mode in order to prevent improper exposure or undesirable consumption of a strobe power supply.
However, it would be difficult in certain situations for the user to determine whether the strobe is to be energized or not each time he is required to do so. If the user could make such a judgment, it would be time-consuming and tedious to change the photographic modes. Sometimes, a shutter chance would be lost, and the user would forget to change the modes, with the result that a photographing error would be caused.
Any photographing error due to the above causes may be prevented by a means for measuring the brightness of the subject prior to being photographed, determining whether strobe light should be emitted, and generating a lightemission inhibit signal when it is decided that no strobe light is to be given off. The light-emission inhibit signal is then delivered to the strobe to prevent the same from generating light output.
As described above, three to four connector terminals or wires have been required for transmitting the conventionally required items of information between the camera and the strobe. Adding another connector terminal for transmitting the light-emission inhibit signal from the camera to the strobe would increase the cost of the strobe. Furthermore, the hot-shoe connector is no longer used for making the necessary connection. The strobe connected somehow for such information transmission would not be handled easily, and would not be compatible with different cameras, but would only be usable exclusively with the camera to which the strobe is connected.